What are the benefits of modifying ECU program (ECU upgrade) or do any harm?

In general, the power increase 8% -36%, lower fuel consumption by 5%-25%, reduce emissions.
A. naturally aspirated models can increase horsepower 10%;
B.TURBO models can increase horsepower 20% -30% or even more;
C. shift more smoothly, the power of convergence even better;
D. solve many problem which the original can not resolved, such as the: low speed easy to turn off and the transmission shift shock etc.
Other else like airbag, oil, radios, odometers, dashboards, immobilizers repair…
To learn morer:CARPROG FULL V4.01